The manufacture of an integrated circuit involves a plurality of operations on wafers of semiconductor substrates. Some of the operations may include processing steps such as photolithography, etching, exposure, as well as inspection and testing of the wafer as it is being formed into the desired end product. Some of these operations involve automated material handling and processing using robotic end-effectors. Many of these operations require a clean room environment devoid of airborne particulates and other contaminants which would seriously compromise the quality of the end product.
Specialized equipment, such as standard wafer pods, have been developed to provide the requisite contamination-free storage environment for the wafers during transfer and processing. For example, Front Opening Unified Pods (FOUPS) provide a protective, sealed, contamination-free enclosure for the wafers. Other versions of containers such as Standard Mechanical Interface (SMIF) pods may also be used for handling of semiconductor wafers both inside and outside of clean rooms depending on the size of the wafers. Commonly assigned U.S. patent application entitled “Transport Module”, Ser. No. 08/891,644, filed Jul. 11, 1997, now U.S. Pat. No. 6,010,008 ('008), as well as U.S. patent application entitled “Wafer Carrier with Door”, Ser. No. 678,885, filed Jul. 12, 1996, now U.S. Pat. No. 5,711,427 ('427) disclose wafer containers that have features exemplifying such a FOUP. The specification of these applications is incorporated herein by specific reference.
For wafers in the range of 200 mm and smaller, SMIF pods have been utilized to provide a clean sealed mini-environment. Examples of these pods are shown in U.S. Pat. Nos. 4,532,970 and 4,534,389. As discussed in the '008 patent, such SMIF pods typically utilize a transparent box-shaped shell with a lower door frame or flange defining an open bottom and a latchable door. The door frame clamps onto processing equipment and a door on the processing equipment and the lower SMIF pod door closing the open bottom are simultaneously lowered downwardly from the shell into a sealed processing environment in said processing equipment. A separate H-bar carrier positioned on the top surface inside of the SMIF pod door and loaded with wafers is lowered with the pod door for accessing and processing said wafers. In such pods the weight of the wafers would be directly on the door during storage and transport.
With the advent of the larger and heavier wafers, specifically the 300 mm wafers, the transport modules for such wafers have evolved so that they now utilize a front opening door for insertion and removal of the wafers as opposed to a bottom door that drops downwardly from the module. The door cannot support the load of the wafers, rather a container portion which includes a clear plastic (such as polycarbonate) shell and other members for supporting the wafers molded from a low particle generating plastic (such as polyetheretherketone) carry the load of the wafers. Such container portions necessarily are made from multiple components assembled together. Because electrostatic discharges can damage or ruin semiconductor wafers, static electricity is a continuing concern in the handling and processing of such wafers. To minimize any such generation of potentials which may cause static electric discharges, the carriers are typically manufactured with conventional static dissipative materials such as carbon filled polyetheretherketone (PEEK) and polycarbonate (PC).
Industry standards for such modules require that the module be capable of interfacing with external processing equipment. For example, the module may need to repeatedly and with precision align with a robotic handling means which engages the door on the front side of the module, opens the door, and with the necessary amount of precision grasps and removes specific horizontally arranged wafers. It is critical that the module and the wafers contained within the module be positioned at a particular height and orientation with reference to an external equipment machine interface such that the wafers will not be located and damaged during the robotic withdrawal and insertion of said wafers.
Additionally, due to the high susceptibility of wafers to contamination by particles, moisture or other contaminants it is ideal to have a minimal number of potential entry paths to the interior of the module. Paths or breaks in the plastic between the interior and exterior of the pod such as for fasteners or at the junction of separate component parts of the module are to be avoided, and, if required, the breaks or openings in the module between the interior and exterior are sealed such as by elastomeric seals. Furthermore, the use at any location in the pod of metallic fasteners or other metal parts are highly undesirable in semiconductor wafer carriers or containers. Metallic parts generate highly damaging particulates when rubbed or scraped. Assembly of a module with fasteners causes such rubbing and scraping. Thus, the use of transport modules requiring metal fasteners or other metal parts are to be avoided. Such modules have a path to ground from the wafer shelves to the equipment interface through several different components including metallic screws.
Typically, such containers are constructed by assembling several plastic parts. However, due to inconsistencies in molding plastic parts, assembly of such plastic parts lead to inconsistencies, such as open cracks between parts and the stacking of the tolerances of each individual part leading to undesirable variations in critical dimensions. Additionally, a handle attached to the top of the container provides the means to lift and transport the container. This handle may be used for manual lifting or, as in the case of the heavier containers, adapted for being lifted by a robotic end-effector. In either case, lifting the container using the handle induces stresses in the top wall of the enclosure. If the handle does not distribute the load over a larger area of the top wall, the stress distribution is likely to be localized over a small area near the points of attachment of the handle to the top wall. Depending on this stress profile, the resulting strains could cause a deformation mode of the top wall which distorts the dimensions of the opening on the front side of the module where it engages with the front door leading to the burping of the FOUP/FOSB seal and a breach of the sealed enclosure.